Objective: Previous studies have attempted to characterise the genesis of triggered activity related to early afterdepolarisations. Little is known about their conduction behaviour. This study was designed to examine the origin and conduction behaviour of triggered activations to throw light on the pathogenesis of torsade de pointes.
Methods: Electrophysiological interactions related to triggered activations and early afterdepolarisations between papillary muscle and Purkinje fibres were studied in the guinea pig in a single chambered bath. EDTA (5 mM) in Tyrode's solution was used and microelectrodes were placed in both papillary muscle and Purkinje fibres.
Results: During early superfusion, marked prolongation of action potential duration and early afterdepolarisations occurred in Purkinje fibres but not in papillary muscle. In addition: (1) with prolongation of action potential duration and early afterdepolarisations in Purkinje fibres, triggered activations arose during phase 2 and were conducted to papillary muscle, where they induced activations; (2) the number of papillary muscle discharges increased with the increase in Purkinje fibre action potential duration in a linear correlation; (3) severing a segment of papillary muscle from Purkinje fibres eliminated these papillary muscle activations; (4) some triggered activations did not conduct to papillary muscle; these had smaller amplitude, slower rate of depolarisation (dV/dt), more positive activation voltage, and similar peak voltages compared to conducted triggered activations; (5) a low plateau resulting from electrotonic interaction was recorded at the Purkinje fibre-papillary muscle junction; this plateau may have facilitated conduction of triggered activations.
Conclusions: In this preparation there was a disparity of effect on Purkinje fibre and papillary muscle. Prolongation of action potential duration and repetitive activations due to early afterdepolarisations originated in Purkinje fibres and were conducted to papillary muscle. Purkinje fibre-papillary muscle interactions are of interest in relation to torsade de pointes arrhythmias which are believed to arise from this mechanism.